The present invention relates to a laminated type photosensitive member having at least a charge generating layer and a charge transport layer on an anodized aluminum substrate.
Hitherto, inorganic photoconductive materials, such as selenium, zinc oxide, titanium oxide, and cadmium sulfide, have been used as photosensitive materials for a photosensitive layer in photosensitive member used in electrophotography. However, these materials have a number of shortcomings as such a high degree of toxicity and a poor moisture resistance.
Photosensitive members consisting of photoconductive materials have advantages in respect to film-forming properties, lightweight properties, and cost performance, but on the other hand they have deficiencies in respect to sensitivity, durability, and stability to environmental changes.
Recently, a laminated type of photosensitive members in which its functions of charge generation and charge transport are separated has been proposed, whereby the difficulties with the earlier known photosensitive members using organic photoconductive materials have been substantially eliminated. As a result, organic photosensitive members have been put in practical use and, indeed, rapid advancement is seen today in this area of technology.
A laminated type photosensitive member includes a charge generating layer and a charge transporting layer on an electroconductive substrate made of metallic aluminum, copper, or the like.
The laminated type photosensitive members are required to satisfy various basic requirements, such as charge retainability, high sensitivity, repetition stability, resistance to insulation breakdown, wearing properties, durability, humidity resistance, transferability, cleaning properties, and preserving stability.
Further, laminated type photosensitive members are now used with laser printers as well, and for this purpose they are required to exhibit high image reliability in the process of reversal development, and good repetition stability.
In particular, a conventional binder-type photosensitive member with one layer can't be applied to reversal development on account of high residual potential, but a laminated photosensitive member can satisfy low residual potential.
Prior-art laminated type photosensitive members, in particular, those in which the charge generating layer is comprised of a dispersion film having a dispersed pigment in a resin, have had various deficiencies such as adhesive or coating properties to the substrate, and charge injection from a substrate into a charge transporting layer. Often, properties of the electroconductive substrate have a great bearing upon these problems. Therefore, improvements of the substrate and its charge injection properties and cladding characteristics are needed. As attempts to meet these requirements, photosensitive members incorporating an undercoat layer have been proposed in Japanese Patent Application KOKAI Nos. 30757/1983 and 95744/1983. Also, photosensitive members having an anodized aluminum substrate have been proposed in Japanese Patent Publication No. 30497/1978 and Japanese Patent Application KOKAI Nos. 14841/1983, 41360/1984, and 140947/1986.
However, any of the undercoat layers disclosed in Japanese Patent Application KOKAI Nos. 30757/1983 and 954744 1983 has a difficulty in that its electrical resistance is liable to be greatly influenced by changes in external environmental conditions, particularly, changes in atmospheric humidity, so that fogging may develop in low humidity conditions. If the electrical resistance of the undercoat layer is high, a static charge is applied to the layer, and such charge acts as so-called residual charge, thus causing a fog in images. An undercoat layer is required to meet various such characteristic requirements as above mentioned, but if it is formed of a single kind of resin, no satisfactory undercoat can be obtained. In view of this fact, the resin layer is constructed very thin, or electroconductive powdery materials (such as metallic powder) are dispersed in the resin if required. However, a thin resin layer provides the unsatisfactory performance as an undercoat layer, while an undercoat layer in which metallic powder are dispersed has a deficiency in that its surface characteristics are unsatisfactory because of the roughness of the metallic particles.
Where such prior art laminated type photosensitive members has been applied to a laser printer in particular, it has not been found successful because of very small black spots being produced in a white paper portion during the process of reversal development.
Japanese Patent Publication No. 30497/1978 discloses a photosensitive member having a free-cutting aluminum alloy substrate with an alumite layer formed thereon by anodizing. Japanese Patent Application KOKAI No. 14841/1983 discloses a photosensitive member formed by a process which includes immersing an aluminum substrate in a water bath having a specific resistance of not less than 10 .sup.6 .OMEGA.cm and a temperature of not less than 60.degree. C. Japanese Application KOKAI No. 41360/1984 discloses a photosensitive member having a phthalocyanine deposited film as a charge generating layer and an aluminum substrate so processed that an unsealed anodized film of 4 .mu.m at least is formed thereon. Japanese Patent Application KOKAI No. 140947/1986 discloses a photosensitive member having a barrier layer and a porous layer formed on an aluminum substrate anodized prior to formation of an a--Si film on the aluminum surface. However, none of these publications contain any teaching on a solution to the problem of black spots produced during the process of reversal development in the case where the charge generation layer is comprised of a dispersion film, or on any relevant conditions.